Figure 7: Gelation of hydrogels using optical control, demonstrating the trapping of MDCK II cells in 3D hydrogels. (a) Initial cell distribution. The two target cells are circled in the inset. Other cells will be flushed away. The inset scale bar is 100 μm. (b) A light pattern (bright circle) is used to trigger hydrogel formation (dark circular area), trapping the target cells. Cells not trapped in the gel are flushed away. (c) The two target cells remain in the 3D hydrogel. (d) Initial cell distribution when using parallel optical patterns to trap MDCK II cells in 3D hydrogels. Four target cells are circled in the inset. Other cells will be flushed away, except those trapped by the second optical pattern. The inset scale bar is 100 μm. (e) Light patterns (bright circles) are used to trigger hydrogel formation (dark circular areas), trapping the target cells while free cells are flushed away. (f) The four target cells remain in the 3D hydrogel.